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a fixed point and determining its temporal evolution. Lagrangian current- 

 measuring devices are often used in circulation studies, pollution studies, and 

 for monitoring ice drift. For Eulerian or fixed current meters, proper place- 

 ment is essential for adequately determining sediment transport pathways. 



Several types of current sensors are in common use including impeller, 

 electromagnetic, acoustic, acoustic Doppler, laser Doppler, and inclinometer 

 types (Fredette et al. 1990). Impeller current measurements are acquired by 

 means of a propeller device which is rotated by current flow. Impeller 

 devices are considered to be the least expensive and have been widely used for 

 a considerable time (Teleki, Musialowski, and Prins 1976). They are subject 

 to snaring, biofouling, and bearing failure, but are more easily repaired in the 

 field and more easily calibrated than other types (Fredette et al. 1990). 



All the other current meters have several features in common, although 

 they operate on different principles. Each has no moving parts, has rapid 

 response, is self-contained, can be used in real-time systems, and can be used 

 to measure at least two velocity components. The degree of experience of the 

 persons working with the instruments probably has more to do with the 

 performance of the current meters than does the type of meter used (Fredette 

 et al. 1990). 



In addition to direct current measurements, indirect current estimates of 

 current speed and direction can also be made from bedforms, particularly in 

 shallow water. The deviations from a flat bed and associated sedimentary 

 structures are associated with coastal hydrodynamics, including the effects and 

 interaction among tidal currents, wave characteristics, and longshore drift, 

 particularly at inlets and estuaries. Bedforms reflect flow velocity, but are 

 generally independent of depth (Clifton and Dingier 1984; Boothroyd 1985). 

 Bedform can vary in response to increasing flow strength (Hayes and Kana 

 1976). Bedform orientation and associated slipfaces also provide clues to flow 

 direction. 



Knowledge of the magnitude and direction of currents at the coast allows 

 the prediction of sediment movements and thus is basic to an understanding of 

 landform development. Information concerning cross-shore (shore-normal) 

 currents and sediment transport can assist in predicting beach profile change. 

 Longshore (shore-parallel) currents and associated transport can assist in 

 predicting beach planview changes. The combined effects of both types of 

 currents, generating cell circulation, may explain or assist in identifying 

 regularly spaced features along many coasts. The longshore migration of such 

 cells can also cause landform migration associated with the spatiotemporal 

 migration of higher energy nodes. 



Conversely, the configurations of the shoreline can provide information 

 regarding littoral currents. Shoreline proturberances, particularly in the 

 vicinity of structures, headlands and barriers, and tidal inlets are useful 

 indicators of the prevailing littoral sediment drift (Komar 1976). Such 

 indicators cannot generally be used for quantitative estimates of the sediment 



Chapter 4 Investigation of Environmental Factors 



